Hubble Telescope Watches Asteroid Whirl Itself to Pieces

For the first time, astronomers have watched a space rock in the main asteroid belt crumble to bits, thanks to the Hubble Space Telescope and a little advance planning.

"Seeing this rock fall apart before our eyes is pretty amazing," UCLA's David Jewitt, who led the cosmic forensics team, said in a news release issued Thursday.

Jewitt and his colleagues first noticed the fuzzy, dusty object now known as P/2013 R3 in September, and followed up with observing time on Hubble over the months that followed. Hubble imagery revealed 10 rocky objects embedded in a dusty envelope that's nearly as wide as Earth. The largest fragment is estimated at up to 400 yards (meters) wide, and each of the objects has a coma and a cometlike tail of dust.

The fragments are drifting away from each other at a speed of roughly 1 mph (1.6 kilometers per hour). That slow disintegration suggests that the asteroid has fallen prey to what's known as the YORP effect. Subtle differences in the absorption of sunlight cause the asteroid's rotation rate to rev up. The resulting centrifugal force puts added stress on the asteroid's loosely bound structure, causing it to crumble like a dry cookie.

Last year, Jewitt and other astronomers spotted an asteroid that sprouted six cometlike tails — apparently due to a similar effect involving solar radiation pressure. They're starting to think this is one of the principal ways in which small asteroids bite the dust, so to speak. Eventually, they expect P/2013 R3's estimated 200,000 tons of debris to turn into myriads of meteoroids — some of which may blaze across Earth's skies as meteors.